Salt, sea water, and brackish water is a favorite habitat for marine organisms. Though small when they enter the port of a cooling tower, these marine organisms remain in the cooling system and grow and become a nuisance or destroy or incapacitate the cooling system structures. The problem at the cooling tower is duplicated in other surroundings. Thus, in places where sea water is used, or in the so-called Tidewater area of Virginia where a brackish water prevails, especially in the York and James Rivers, marine fouling is a major problem.
The exact mechanisms of marine fouling on clean surfaces are not completely understood; however, substrates exposed to saline waters are initially covered by slime-forming microorganisms. The first step is the attachment of capsulated bacteria, diatoms and some protozoa. In velocity areas of cooling systems, the slime layer forms a film for subsequent attachment by higher organisms. Low velocity areas of cooling systems may include trash racks, strainers, screens and other components of intake structures, pump structures, approach conduits and tunnels, blends in piping, manhole access tunnels, condenser water boxes and tube sheets. Usually, the water velocity where macrofouling attachment occurs is less than 4 feet/second. Primary marine fouling organisms (such as barnacles, bryozoans and hydroids) follow almost immediately after the development of the slime film when their larvel forms are present in the ecosystem. These are later joined by secondary fouling organisms, such as anenomes and mussels. The primary foulers appear to alter the conditions of the surface, so that it is more suitable for settlement of the secondary foulers. This rapid succession of foulers ultimately leads to an equilibrium or climax condition characteristic of the locality and substrate.
Barnacles have a worldwide distribution and are one of the most common fouling organisms, with numerous species occurring along the coastline of the United States. Of the many organisms which have been found in sea water culverts, the barnacle has proven to be the most troublesome. Barnacle larvae can attach themselves to a solid surface under higher rates of fluid shear than any other animal (8.9 feet/second); their presence then forms a roughness which reduces local shear to values at which settlement of other species can recur.
Most barnacles are hermaphroditic (containing both male and female sexual organs in the same individual). Egg fertilization occurs internally and development proceeds within the adult until the larvae are released as free-swimming nauplii. During a period of active swimming and growth, the barnacle nauplius moults several times into slightly different forms until transformation into a cyprid larvae. The cyprid invades cooling water systems and settles on a suitable substrate. Once settled, the cyprid secretes a cement and begins to build its shell. During the initial stage of shell formation, the barnacle may detach if conditions are unfavorable. However, once an easily recognized shell is formed, the barnacle is incapable of locomotion.
It has been shown that cyprid larvae that have settled on a substrate can cement themselves permanently within 18 minutes and that metamorphosis to the juvenile stage occurs within 20 hours.
The most common fouling barnacles belong to the genus Balanus, with several species occurring on each coast of the United States. Balanus belongs to the general group of barnacles referred to as acorn barnacles, which include all those whose shells are attached directly to the substrate. Unlike the goose barnacles, whose attachment to a substrate is a muscular stalk which disintegrates after death, acorn barnacle shells remain firmly attached even after death. This permanent attachment makes the acorn barnacle more of a problem to control.
As used herein, the term macrofoulant defines primary and secondary marine fouling organisms including but not limited to barnacles, bryozoans, hydroids, anenomes, mussels, cyprids, mollusks, and the like.
The present invention uses for certain marine organisms that which has previously been patented for fresh water and for controlling asiatic clams, U.S. Pat. No.4,643,835 Koeplin-Gall, et al (Nalco). The dosage is the same where the proportion of bromide salts to chlorine as hypochlorous acid is from about 0.25 to about 1.5 equivalents. The chlorine can be in the form of a liquid chlorine. Such chlorine solutions can be prepared by the dissolution of gaseous chlorine in water, forming through hydrolysis hypochlorous acid and hydrochloric acid. Chlorine solutions of sodium hypochlorite will also work. By the term "aqueous chlorine solution" as used herein is meant solutions equivalent to that derived from dissolution of chlorine in water or acidic solutions containing chlorine as the hypochlorous acid or solutions of sodium or calcium hypochlorite.
Bromide may be substituted for potassium bromide in the composition, such as by using sodium bromide. One feature of the combination forming the composition of the present invention is the formation of hypobromous acid by the displacement of at least some chlorine of the hypochlorous acid with bromine derived from the bromide salt, forming a generally innoxious chloride salt by-product. Thus, the composition is a combination which includes at least some hypobromous acid and is thus more effective in typical water systems at least due to the greater activity of bromamines over chloramines that are formed when ammonia is present in the system. The composition of the present invention results in effluent discharges of lower toxicity due at least to the greater instability of bromine residuals.
The degree of conversion is hypochlorous acid to hypobromous acid depends of course to an extent on the relative proportion of bromide salt to hypochlorous acid which are combined to form the composition and other factors affecting the displacement of chlorine with bromine. The present invention encompasses not only a complete or near complete displacement of bromine for the chlorine in the hypochlorous acid, providing essentially a bromination system, but displacement far short of this.
Also, it is necessary to have a biodispersant which may be about 10% of the total composition. The biodispersant may be ethylene oxide condensates with propylene oxide adducts or propylene glycol having an HLB between 4-10 and a molecular weight between 1,000-5,000, nonionic polyethoxylated straight chain alcohols, tris cyanoethylated cocodiamines, polyoxyethylene sorbitan ester/acids, nonionic N,N, dimethyl stearamides, nonionic amine polyglycol condensates, and nonionic ethoxylated alcohols, and mixtures thereof.
The problems in fresh water with asiatic clams are not duplicated by the problems here in salt water as in removing barnacles and mussels.
With relation to the combination biocide, the solution contains a bromide salt and a biodispersant designed to improve chlorine activity. Such a combination combining sodium hypochlorite and the present invention meets all the criteria for a preferred biocide; it is environmentally accepted, safe to handle, and easy to feed.